US1729339A - Alloy of magnesium - Google Patents

Description

sept.- 24, 41929. J, A, GANN 1,729,339

ALLVOY MGNESAIUM Filed 001?. 27. 1921 f9.7??? .7a @am BY ATToRNEw" Patented Sept.Y 24, 1929iA UNITED STATES-PATENT OFFICE JOHN A. GANN, F HIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CIIEMICAL COM.'-

PANY, or'l MIDLAND,

MICHIGAN, A CORPORATION OF MICHIGAN i ALLOY OF MAGNESIUM Applicatioaledpctober 27, 1921. Sei-ia] No. 510,795.

The present improved alloy is one in which magnesium is the predominant element, the

object being to develop anl alloy that will possess the characteristic lightness which is obtained by the use of magnesium in excess of 80%, while such alloy will be characterized by high strength and toughness, as well as have a high melting point and high thermal conductivity.

The eldof use in the mechanical arts to which an alloy possessing the lightness and physical characteristics enumerated above may be applied need not be described in detail for the purpose in hand, especiallywhen it is added that the particular alloy hereinafter described possesses the added quality of mechanical workability, i. e., itmay be readily forged or shaped under pressure, rolled into sheets or drawn. Where hardness rather than softness may be considered desirable, as, for example, where the metal is to -be used in pistons of internal combustion engines this characteristic may be improved by adding one or more otherv metals in varying quantities, as will be hereinafter explained, the present invention consisting of an alloy of magnesium and cadmium with or without the addition of such further metals, together with the steps involved inthe making of such alloy hereinafter fully described and particularly pointed out in the claims. The annexed drawing and following description, it will be understood, set. forth but several of the various ways in which the invention may be carried out. Y

In said/annexed drawing The single gure there appearing is a diagrammatic representation of certain` physical properties discovered in a binary magnesiumcadmium alloy of the class in hand. In such diagrammatic figure, the physical properties represented, it will be noted,are the impacttoughness, hardness and tensile strength, the

-hardness being determined by the Brinell method and scaled to correspond with the imact-toughness, the latter being determined y the single-blow method. While such impact-toughness drops rapidly up to the addition of 4per centof cadmium, it will be l 'observed that from this point on the curve becomes much less steep with the addition of more cadmium'. The tensile strength, on the contrary, increases rapidly at first and then at a rate approximately inverse to the rate of decrease inv impact-toughness. Thel Brinell hardness increases slowly and at a practically constant rate throughout the range under consideration, which I place at between 5% and 10%` of cadmium in order to secure a proper balance in respect to the characteristics in question. v

The resulting alloy, where between 5% and of cadmium is thus utilized, the balance being magnesium, will have a specific gravity varying from approximately 1.8 to 1.9; tensile strength, from 19,000 to 20,500 per square inch; Brinell hardness, from 44 to 45 and single blow impact-toughness from 90 to 5.

Where the alloy is to be used for pistons in internal combustion engines, or under conditions involving similar strains and temperatures, I have found that the addition of a small proportion of aluminum or of aluminum and copper is advantageous in that it imparts increased hardness in the result'- ing product. A satisfactory formula for such aternary alloy in which aluminum is the third ingredient is las follows, viz magnesium 88%, cadmium 8% and aluminum 4%; for such a ternary alloy in which copper is the third ingredient the preferred formula is as follows, ving-magnesium 94%, cadmium 4% and copper-2%; while for an alloy including bothjaluminum and copper the following composition is recommended, viz magnesium 88%-, cadmium 6%, aluminum 4% and copper 2%.

Even where the proportion of aluminum thus added is greater-than that of the cadmium, as in the following formula, viz,

Amagnesium aluminum 8%,copper 1% above as having been discovered in the simple binary alloy ofmagnesium and cadmium will be retained -to a perceptible degree. This may be attributed to the fact that cadmium forms a solid solution with ma nesium throughout the whole series ofl possife combinations. In other words, there is no eutectic present whatever' the proportion of ycadmium. A relativelyv high meltingpoint is also obtained, as well as a high thermal conductivity, the latter being 0.304, where the proportion of cadmium is 12%, or only a little less than the thermal conductivity of pure magnesium, and correspondingly nearer that of magnesium where the proportion of cadmium is less. So far as concerns impacttoughness, as determined by the single blow method in the range beyond 5% of cadmium and up to 20%, the present binary alloy shows greater toughness than any binary magnesium alloy with another metal present in corresponding amount.

To make my improved alloy a measured quantity of pure magnesium metal is first melted in a suitable pct along with a proper amount of flux that, while heavier than such metal, will have proper surface tension to properly and eectively coatthe metal. As an example of such a flux, approximately equal parts of anhydrous magnesium chloride and sodium chloride may be employed and if the specific gravity of such flux proves inadequate to float the metal after it has been alloyed, a small amount of barium chloride may be added. A small amount of the molten magnesium metal is then taken up into the ladle and all or a part of the cadmium, depending on the total percentage of the latter to be added to the batch, is first placed in such ladle and melted with the magnesium therein, thereby producing an alloy relatively high in cadmium. The contents of the ladle are then gradually added to the main body of molten magnesium, with the result that the cadmium will diffuse throughout the mass and not drop into the body of flux on which the latter floats and so be lost. the introduction of the cadmium alloy has been effected, the whole mass is then well puddled, and the operation may then be regarded as complete and the molten alloy cast either into ingots or directly into the form of mechanical parts, such as pistons or the like, for which it is intended to be used.

Where aluminum, or aluminum and copper, or other metals are to be added to the binary alloys in accordance with the illustrative'formulas hereinbefore given, such additional metal or metals may be separately introduced in the same fashion as the cadmium, or they may be at once added along with the cadmium informing the preliminary alloy which is subsequently added to the main bodyA Vof the molten magnesium metal, resulting in the production of an alloy in which magnesium is the predominant ingredient. Again, in some cases it may be found more advantageous to add to the magnesium alloy in the Lladle a magnesium alloy rich in the alloying metal,`instead of such metaly itself.

For convenience inl defining the relative proportions of the metalsthat-enter intofthe As soon as,

alloy, the magnesium may be referred to as present in predominant amount, meaning an amount on the order of per cent or more of the total; while in referring to the presence of other constituents in substantial but relatively small amounts, it will be understood that amounts are meant on the order of those specified in the formulas hereinbefore set forth, due regard being given to thel fact that the total of such other ingredients will decrease as the amount of the predominant constituent is increased.

AOther modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the steps herein disclosed or the ingredients employed in carrying out such steps, pro-` vided the steps or ingredients set forth in the following claims, or the equivalent of such steps or ingredients be employed.

I therefore particularly point out and distinctly claim as my invention l. As a new product, an alloy containing from ninety to ninety-live per cent of magnesium and between ten and five per cent of cadmium.

2. As a new product, an alloy containing magnesium, cadmium, aluminum and copper, wherein the magnesium largely predominates and the remaining constituents are present in substantial but relatively small amounts.

3. As a new product, an alloy containing magnesium, cadmium, aluminum and copper, wherein the magnesium largely predominates and the remaining constituents are present in substantial but relatively small amounts, the cadmium being the principal otheringredient.

4. As a new product, an alloy containing approximately the indicated percentages of the following metals, viz:--magnesilrm eighty-eight per cent, cadmium eight per cent and aluminum four per` cent.

5. rlhe method of making a magnesiumcadmium alloy, which consists in first interfusing the desired amount of cadmium with a relatively small quantity of magnesium, and then adding :the resulting alloy to the remaining quantity of magnesium in molten I state.

6. The method of making a magnesiumcadimum alloy, wherein the magnesium largely predominates, which consists in irst interfusing the desired amount of cadmiumv with a relatively small quantity of magnesium, whereby an alloy high in cadmium is produced, and then adding such resulting alloy to the remaining quantity of magnesium.

Signed by me this 24th d ay of October,

1921. JOHN A. GALNN..

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